IMO the 2 best cards for linux are the Senao NL-2500 and the Ubiquiti SRC 300mW. They both have two connections for dual antennas and work well with Backtrack and Ubuntu. Great for aireplay when cracking wep. You can get them here:

No problems so far. I have been experimenting with Ubuntu a lot lately and all my tools are working well with this card. If you want to experiment with AP phishing at a wireless hotspot ( assuming you were asked to test it of course) you need a card with some power.